1. Field of the Invention
The present invention relates generally to optical pickup devices used for recording and reproducing information on and from optical discs such as compact discs (CDs), digital versatile discs (DVDs), or Blu-ray discs (BDs), or to optical disc drive units with a built-in optical pickup device. More particularly, the invention is directed to a technique for adhesion fixing of laser diodes, light-receiving elements, and the like.
2. Description of the Related Art
The optical pickup devices used to record and reproduce information on and from optical discs, or optical disc drive units with such a built-in optical pickup device, usually include two kinds of optical systems. One kind of optical system guides the light that has been emitted from a laser diode (LD), to an objective lens via various lenses, prisms, reflecting mirrors, and other optical elements, and converging the light upon an optical disc. The other kind of optical system converts the light that has been reflected from the optical disc, into image form on the surface of the light-receiving element via the objective lenses, the prisms, the reflecting mirrors, various lenses, and the like. Of these optical elements, at least the LD and the light-receiving element need fixing after being adjusted to an optically optimal position relative to a casing of the optical pickup device. For this reason, the LD and the light-receiving element are usually constructed so that both are temporarily bonded onto respective holders suitably shaped for bonding onto a casing, then the holders and the casing are each adjusted to an optically optimal position, and the holders are fixed to an optimal three-dimensional position on the casing by utilizing the thickness of an adhesive agent layer formed using an ultraviolet (UV) curable adhesive.
In this case, the clearance between the casing and the holder to which the LD or the light-receiving element is fixed, that is, the thickness of the adhesive layer is often maximized to about 1 mm due to characteristics of optical components and any nonuniformities in machining tolerance and assembly position between optical components. This may cause nonnegligible curing shrinkage of the adhesive itself during UV irradiation, resulting in significant optical misalignment. Avoiding this problem requires an adhesion-fixing technique that allows any shifts in position due to the shrinkage of the adhesive itself to be suppressed, even if the bonding clearance between the holder and the casing is large.
JP-A-2005-32314, for example, discloses the features of a technique that even when a laser light-emitting element or a light-receiving element is to be fixed with a clearance relative to a frame, using an adhesive mixed with inorganic compound powder for letting UV radiation through makes it possible to suppress any shifts in position by suppressing fluidic deformation during curing, as well as to apply a necessary amount of UV irradiation.
JP-A-2004-10759 discloses a structure in which either a first member or a second member has protrusions, with the other having connections disposed adjacently to these protrusions to render positions of each protrusion adjustable in a height direction thereof. In this structure, the first member and the second member can be adhesion-fixed via a desired clearance by applying a thin coat of adhesive to a region from the protrusion to the adjacent connection and then curing the adhesive.
JP-A-2002-251776 discloses a structure in which a mounting plate for a photodetector is notched inward from both ends of the plate to prevent emitted UV radiation from easily forming a blind region that cures the adhesive. In addition, surfaces onto which the notches are to be bonded in the structure are each grooved in parallel to a surface direction of the mounting plate, such that a direction in which the adhesive is likely to shift in position is set to match a direction of the grooves.